Experimental Infection of Ticks with R. rickettsii | CDC EID

EID Journal Home > Volume 17, Number 5–May 2011

Volume 17, Number 5–May 2011
Research
Experimental Infection of Amblyomma aureolatum Ticks with Rickettsia rickettsii
Marcelo B. Labruna, Maria Ogrzewalska, João F. Soares, Thiago F. Martins, Herbert S. Soares, Jonas Moraes-Filho, Fernanda A. Nieri-Bastos, Aliny P. Almeida, and Adriano Pinter

Author affiliations: University of São Paulo, São Paulo, Brazil (M.B. Labruna, M. Ogrzewalska, J.F. Soares, T.F. Martins, H.S. Soares, J. Moraes-Filho, F.A. Nieri-Bastos, A.P. Almeida); and Superintendency of Control of Endemic Diseases, São Paulo (A. Pinter)

Suggested citation for this article

Abstract
We experimentally infected Amblyomma aureolatum ticks with the bacterium Rickettsia rickettsii, the etiologic agent of Rocky Mountain spotted fever (RMSF). These ticks are a vector for RMSF in Brazil. R. rickettsii was efficiently conserved by both transstadial maintenance and vertical (transovarial) transmission to 100% of the ticks through 4 laboratory generations. However, lower reproductive performance and survival of infected females was attributed to R. rickettsii infection. Therefore, because of the high susceptibility of A. aureolatum ticks to R. rickettsii infection, the deleterious effect that the bacterium causes in these ticks may contribute to the low infection rates (< 1%) usually reported among field populations of A. aureolatum ticks in RMSF-endemic areas of Brazil. Because the number of infected ticks would gradually decrease after each generation, it seems unlikely that A. aureolatum ticks could sustain R. rickettsii infection over multiple successive generations solely by vertical transmission .

The bacterium Rickettsia rickettsii is the etiologic agent of the deadliest rickettsiosis, Rocky Mountain spotted fever (RMSF), which is referred to as Brazilian spotted fever in Brazil (1). The distribution of R. rickettsii is restricted to the Americas; confirmed cases of RMSF have been reported in Canada, United States, Mexico, Costa Rica, Panama, Colombia, Brazil, and Argentina. Different tick species have been implicated as vectors of R. rickettsii in different geographic areas. Whereas the ticks Dermacentor andersoni and D. variablilis are the main vectors in the United States, the Amblyomma cajennense tick is the most common vector in South America (1,2). The tick Rhipicephalus sanguineus has also been implicated as a vector for R. rickettsii in a few areas in Mexico and the state of Arizona in the United States (2,3). However, A. aureolatum ticks are the main vector in the metropolitan area of São Paulo, Brazil, distinguishing this area from the remaining RMSF-endemic areas of Latin America (1,4,5).

Adult A. aureolatum ticks feed chiefly on Carnivora species (mostly domestic dogs), but immature ticks (larvae, nymphs) prefer to feed on passerine birds and a few rodent species (6). Humans have reported being attacked only by adults, usually by a single tick (7), because population density of A. aureolatum ticks is usually low (8). One field study in an RMSF-endemic area of São Paulo found that <1% of the A. aureolatum adult ticks were infected by R. rickettsii (5). The reasons for such a low infection rate are not clear; a recent laboratory study reported that up to 100% of A. aureolatum larvae efficiently acquired and maintained the R. rickettsii infection to the nymphal stage, after a larval feeding on experimentally infected guinea pigs (9). Therefore, we evaluated the transstadial maintenance and transovarial transmission of R. rickettsii in A. aureolatum ticks through 4 consecutive generations of this tick in the laboratory; the vector competence of larvae, nymphs, and adults; and deleterious effects of R. rickettsii on the survival of larvae and nymphs and on the reproductive performance of female ticks. full-text: Experimental Infection of Ticks with R. rickettsii | CDC EID


Suggested Citation for this Article
Labruna MB, Ogrzewalska M, Soares JF, Martins TF, Soares HS, Moraes-Filho J, et al. Experimental infection of Amblyomma aureolatum ticks with Rickettsia rickettsii. Emerg Infect Dis [serial on the Internet]. 2011 May [date cited].
http://www.cdc.gov/EID/content/17/5/829.htm


DOI: 10.3201/eid1705.101524


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Marcelo B. Labruna, University of São Paulo, Faculty of Veterinary Medicine, Av. Prof. Orlando Maques de Paiva 87, São Paulo, SP, Brazil 05508-270; email: labruna@usp.br